This invention relates to nail like inserts in the air vents of tire molds.
Two basic types of tires are presently being built. Bias ply tires, the first type, are built as cylinders on tire building drums. The cylinders are placed in molds. A bladder positioned inside of the cylinder is inflated with steam to convert the cylinder to toroidal shape, force the uncured rubber of the outer surface of the tire into the mold configuration and cure the tire. The procedure employed for molding a radial tire is much the same except that the uncured tire is in the shape of a toroid having a diameter almost as large as the inner surface of the mold prior to insertion into the mold. After curing it is very difficult to remove a radial tire from a conventional two piece mold because the outer diameter of the radial tire is larger than the inner diameter, formed by the surface protrusion, of the mold. By a two piece mold is meant one having two pieces against which the outer surface of the tire is formed. A bladder expands the tire into the mold surface. A tire is normally molded lying in a horizontal plane.
The upper mold surface is lubricated with silicone to facilitate release. To remove the tire from the mold a radial tire is forced from the bottom half of the mold with considerable pressure. The radial tire releases suddenly. When the tire breaks loose some of the rubber protrusions formed in the air vents break from the tire and collect in the bottom half of the mold. The broken off rubber protrusions are hereinafter referred to as plugs. Attempts to remove the plugs with pressurized air have been effective in 90% of the cases on one line of radial tires resulting in 10% of the tires produced of that line containing cosmetic surface defects caused by plugs lying in the bottom half of the mold being molded into the sidewall of the next tire cured in the mold.
The prior art does not appear to recognize the problem of rubber plugs breaking off of tires and being molded into the sidewalls of subsequently formed tires.
Even if the plugs formed in the mold vents do not break off, they are undesirable both in bias and radial tires. The plugs that do not break off the tire are usually removed by hand using knives. This is a waste of rubber and often results in the tires being cut in the wrong places by the knives. This trimming can result in the tire being thrown out of balance.
The trimming of the plugs from tires requires a large amount of hand labor. When dealing with rapidly spinning small tires such as a truck or automobile tire, there is the danger of the rotating tire suddenly taking on a forward motion and striking the trimmer. With a large tire such as a farm implement tire or a giant earth mover tire there is the problem of physically moving the tire for the trimmer to remove the plugs and the problem of the large tire striking the trimmer when the tire is moved and/or rotated. When tires are manufactured in segmented molds there is also the problem of the rubber plugs, formed in the vents, breaking off and getting in the complex mechanical mold mechanism. This could cause mechanical wear or early failure of the segmented mold mechanism.
British Pat. No. 922,788 discloses the use of a valve to eliminate spew or plugs so as to eliminate a subsequent finishing operation.
Other patents such as U.S. Pat. Nos. 3,822,857 and 3,804,566 show the use of small openings in the vents apparently to allow air to pass but little if no rubber.